Magenta color image forming couplers which are widely used in practice and which have been intensively studied are the 5-pyrazolone type couplers It is known that dyes formed from 5-pyrazolone type couplers have excellent fastness to heat and light, but they have an undesirable absorption of the yellow component in the region around 430 nm, which causes color turbidity.
In order to decrease the yellow component absorption, a pyrazolobenzimidazole nucleus as described in British Patent 1,047,612, an indazolone nucleus as described in U.S. Pat. No. 3,770,447 and a pyrazolotriazole nucleus as described in U.S. Pat. No. 3,725,067 have been proposed as a magenta color image forming coupler skeleton.
The inventors have developed pyrazoloazole type magenta couplers including, for example, imidazo[l,2-b]pyrazoles, pyrazolo[1,5-b][l,2,4]triazoles, pyrazolo1,5-d]tetrazoles, pyrazolo[l,5-d]benzimidazoles and pyrazolopyrazoles. These pyrazoloazole type magenta couplers have good color-forming properties and form magenta dyes having little undesirable yellow absorption.
However, azomethine dyes formed from these pyrazoloazole type magenta couplers have relatively low fastness to light and humidity and heat. Moreover, when these azomethine dyes are exposed to light for a long period of time or preserved under high temperature and high humidity, color fading or discoloration of the dye images occurs, resulting in degradation of the image quality. Such color fading of the image is a fatal defect for recording materials. In order to overcome this problem, it has been proposed to selectively employ couplers less susceptible to color fading or to employ color fading preventing agents which can prevent color fading due to light.
In particular, the image degradation preventing effect of color fading preventing agents is large. It is already known that compounds obtained by etherification of a phenolic hydroxy group exhibit an excellent effect on preventing the color fading of dyes formed from pyrazoloazole type magenta couplers. For example, there are known diether type compounds obtained by dietherification of hydroquinones as described in U.S. Pat. No. 4,588,679, JP-A-59-l25732, JP-A-60-262l59, JP-A-282845, JP-A-6l-292l44 and JP-A-6l-275842 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), methylenedioxybenzenes as described in JP-A-6l-269l54, ethylenedioxybenzenes as described in JP-A-63-l304l, spiroindanes as described in U.S. Pat. No. 4,360,589, JP-A-6l-282840 and JP-A-62244046, and spirochromans as described in JP-A-62-4045.
These compounds are excellent as color fading or discoloration preventing agents for dye images. However, they are still undesirable because the requirement of the fastness of the dye images has greatly increased with time.
The inventors have investigated in detail compounds obtained by the etherification of phenols and hydroquinones as described in the above patents in order to achieve sufficient fastness of a magenta color image formed from pyrazoloazole type magenta couplers. As a result, it has been surprisingly found that hydroquinone diether compounds having substituents on both the 2-position and 3-position thereof exhibit an extraordinarily large improving effect on fastness which can not be attained by other known hydroquinone diether type compounds.